Index error - Threads

[FredericWantiez]

I'm trying to run some of the tests model in Turing with the new Libtask but run into an index error:

  Got exception outside of a @test                                                                                                      
  MethodError: no method matching getindex(::Libtask.Box{Nothing}, ::Int64)                                                             

The IR looks like this:

DynamicPPL.Model{var"#normal#21", (), (), (), Tuple{}, Tuple{}, DynamicPPL.DefaultContext}(:normal, var"#normal#21"(Core.Box(var"#normal
#21"(#= circular reference @-2 =#))), NamedTuple(), NamedTuple(), DynamicPPL.DefaultContext())                                          
1: (%1, %2, %3)                                                                                                                         
  %9 = Libtask.Tape()                                                                                                                   
  %10 = Libtask.run_and_record!(%9, Libtask.box_args, %2, %3)                                                                           
  %11 = Libtask.run_and_record!(%9, Base.indexed_iterate, %10, 1)                                                                       
  %12 = Libtask.run_and_record!(%9, Core.getfield, %11, 1)                                                                              
  %13 = Libtask.run_and_record!(%9, Core.getfield, %11, 2)                                                                              
  %14 = Libtask.run_and_record!(%9, Base.indexed_iterate, %10, 2, %13)                                                                  
  %15 = Libtask.run_and_record!(%9, Core.getfield, %14, 1)                                                                              
  %4 = Libtask.run_and_record!(%9, Base.getproperty, DynamicPPL.Threads, :nthreads)                                                     
  %5 = Libtask.run_and_record!(%9, %4)                                                                                                  
  %6 = Libtask.run_and_record!(%9, DynamicPPL.:(==), %5, 1)                                                                             
  %17 = Libtask.val(%6)                                                                                                                 
  br 3 unless %17                                                                                                                       
2:                                                                                                                                      
  %7 = Libtask.run_and_record!(%9, DynamicPPL.evaluate_threadunsafe, %1, %12, %15)                                                      
  return %7                                                                                                                             
3:                                                                                                                                      
  %8 = Libtask.run_and_record!(%9, DynamicPPL.evaluate_threadsafe, %1, %12, %15)                                                        
  %16 = Libtask.run_and_record!(%9, Base.identity, %8)                                                                                  
  return %9                                                                                                                             

From what I understand DynamicPPL branches on the number of threads here:

function evaluate!!(model::Model, varinfo::AbstractVarInfo, context::AbstractContext)
    return if use_threadsafe_eval(context, varinfo)
        evaluate_threadsafe!!(model, varinfo, context)
    else
        evaluate_threadunsafe!!(model, varinfo, context)
    end
end

but we only intercept one return block in intercept:

last_blk = IRTools.blocks(ir)[end]

[yebai]

@FredericWantiez it's a known issue - the new Libtask does not support branching. We plan to add support for this once the integration tests on the Turing side are fixed and merged.

Related: #96

[yebai]

Probably fixed by #107. Please reopen if otherwise.